This proposal aims to examine the feasibility of using plasminogen activator inhibitor type 1 (PaI-i) mutants as inhibitors of the neutrophil proteinases, neutrophil elastase and cathepsin G. Native PAI-i is not an inhibitor of neutrophil enzymes but preliminary studies presented in this grant show that its specificity can be readily changed by site directed mutagenesis. Apart from inhibiting neutrophil proteinases, other properties of PAI-i make it an attractive candidate for a therapeutic for pathologies involving tissue destruction by neutrophil proteinases. Unlike the endogenous inhibitors of neutrophil proteinases, PAI-i is an effective inhibitor of surface bound proteinases. In addition, PAI-i in complex with proteinases is cleared by receptor-mediated endocytosis more efficiently than the endogenous inhibitors. Our colleagues at the Holland Laboratories of the American Red Cross demonstrate that a single amino acid mutation in reactive center bond of PAI-i converts it to an effective inhibitor of pancreatic elastase without affecting receptor-mediated endocytosis. Based on these findings we propose to design and produce specific PAI-i mutants that inhibit the neutrophil elastase and cathepsin G. PROPOSED COMMERCIAL APPLICATIONS: Pulmonary diseases, such as those caused by cigarette smoke and genetic deficiency are associated with serious tissue damage caused by the proteinases neutrophil elastase and cathepsin G. A current therapy for hereditary emphysema (deficiency of alpha one proteinase inhibitor) is replacement with fractions of human plasma containing the missing inhibitor. The current treatment is of limited availability. There are more than 100,000 hereditary emphysema sufferers in the US alone. Development PAI-1 mutants targeted to neutrophil elastase and cathepsin G provide a strong commercialization potential for a superior alternative to current therapies treating emphysema and offer the hope of treating other inflammatory diseases.